Electrical steel and method of making the same



Oct. 28, 1941. O, TT 2,260,397

ELECTRICAL STEEL AND METHOD 01" MAKING THE SAME Filed May 25, 1939 2 Sheets-Sheet 1 y- INVENTOR Y Otho M- Otte B ATTORN EYS Oct. 28, 1941.

.o. M. o'r'rE ELECTRICAL STEEL AND METHOD OF MAKING THE SAME 2 Sheets-Sheet 2 Filed May 25, 1939 as A i INVENTOR Otho M. Otte ATTORNEYS Patented Oct. 28, 1941 UNITED STATES PATENT. OFFICE.

ELECTRICAL STEEL AND METHOD OF MAKING THE SAME Otho M. Otte, Tarentum, Pa.

Application May 25, 1939, Serial No. 275,696

4 Claims.

This invention relates to ferromagnetic materials. It particularly relates to silicon steel having improved magnetic properties, and to a process for preparing the steel so as to increase its magnetic permeability and decrease its hysteresis loss.

In the production of silicon sheet metal, as heretofore practiced, the hot ingot was rolled back and forth in the blooming or clogging mill sired sheet steel, and thesesections were rolled,.

' duction of transformer cores in which the magnetic flux is longitudinal of the strip.

'It has been proposed to improve the magnetic. properties longitudinally of a thin sheet or strip by causing a cold reduction of 61% or more in the thickness of the steel. Because of the tremendous pressures necessary, this heavy cold reduction appears to be practically limited to silicon steel having not more than about 3 /2% silicon,

and even then it is necessary to slit the metal strip into relatively narrow widths suitable for subjection to the pressures necessary for such cold reduction. 1

It is, however, desirable to produce such thin,

long, silicon steel strips with improved Properties,

and having a silicon content of Li or higher.

I steels heretofore produced.

Another objectofthis invention is to provide a process for producing, at a relatively low cost, silicon steel sheet or strip having improved magnetic permeability longitudinally thereof.

A furthercbject of the invention is to provide a process for producing silicon sheet steel or strip having improved magnetic permeability longitudinally thereof, wherein the major reductions in the preparation of the sheet may be accomplished by hot rolling.

The magnetic properties of steel strips in a longitudinal direction are improved with an increased percentage of silicon, but the material becomes increasingly brittle and cannot be advantageously cold worked or processed. It is,

therefore, a furtherobject of this invention to provide a process for producing silicon steel strips or sheetsof high silicon content having still higher magnetic permeability and lower hysteresis loss in directions longitudinally of the strips or sheets, which strips or sheets may be produced by hot rolling. I

A still further object of the invention is to provide a silicon steel of relatively high silicon content and having relativelylow hysteresis loss and high permeability longitudinally of the grain of the sheet or strip.

Other objects will be apparent from the following description of the process and apparatus which may be used, and which is illustrated in the accompanying drawings, in which:

Figure 1 is a schematic elevational view showing the steps of the first pass or the ingot through the cogging or blooming mill;

Fig. 2 is a schematic view showing the positions occupied by the metal during the second pass through the cogging or blooming mill;

Fig. 3 is a further diagrammatic view showing the positions occupied by the ingot in the third or subsequent passes through mill rolls to form a slab or bar of the desired shape;

Fig. 3ais adiagrammatic'view showing one section cut from a bar or slab'in such manner as to readily designate the proper entry end for further operations;

Fig. 4 is a diagrammatic elevational view of the metal of Fig. 3 during further steps in its reduction;

Fig. 5 is a diagrammatic view showing the recalling of the strip so that the end portion A is on the outside of the coil;

Fig. 6 is adiagrammatic view of the coiled strip of silicon steel obtained from the apparatus of Fig. 5;

Fig. 7 is a schematic, elevational view of the metal during further steps in its reduction;

Fig. 8 is a. diagrammatic view showing flow lines of the metal during reduction between rolls;

Fig. 9 is a diagrammatic view showing the relareducing pass in the blooming mill, and each re ducing pass in subsequent rolls, is made unidirectionally, i. e., in the same sense. Thus, according tothis invention, if the end of the ingot first presented for the reducing pass to the blooming millbe designated A, and the opposite end be designated B, the metal of the ingot is always introduced for reducing passes through subsequent reducing 10115 in the. direction of A to n, so that it passes therethrough in the same sense, i. e., from A to B. The back-and-forth' rolling of the metal, even in the blooming mill, and in subsequent reducing mills, does not appear to give the proper orientation of crystal axes or grain arrangement in the metal to obtain the improvedmagnetic properties. I L

In this application the term sense is being used to mean in one longitudinal direction. In other words, in the making of reducing passes, to reduce the metal from the ingot to the strip of final thicknessflghe ingot, slab, ba'r, sheet or strip, as may, in turn, be prepared, is presented to the rolls in the same relative position end-toend as the original ingot was first presented to blooming mill rolls.

Referring to the drawings, the ingot I or silicon "steel, which has been stripped in the usual manner from the ingot mold and reheated in the usual manner in a soaking pit to obtain a uniform, temperature. throughout, and having end portions A and B, respectively, is passed between the rolls I and 2 of the blooming mill to elongate it as desired to form the 'reduced ingot M having end portions 'A and B, corresponding with por-. tions designated-A and B of the ingot. The metal M is then returned to the position shown in Fig. 2, so that the end A may again enter the bite of the rolls I and 2 of the blooming mill. The re- .tum of the metal M from the position of Fig. 1 I to that of Fig. 2 may be accomplished by raising roll I of the blooming or cogging mill to allow a dead pass of the metal M therethrough, and using the table rolls to cause the metal to return to the initial position: If the metal .is caused to pass through the rolls I and 2 in a sense .from B to A, all pressure. should be removed Iromthe rolls, so that no reduction of metal takes place. Other suitable means, such as providing a shunt or byensure the presentation of the proper end of the metal to the rolls.

and the metal passes therethrough in a sense from A to B.

During the rolling operations the metal may be trimmed in the usual manner and, if the quantity of metal is too great for further handling, the

slabs S, or the bar, as the case may be, maybe cut, as desired, into sections of the desired size or weight. In suchcases, however, it is desirable The slab or bar S, diagrammatically indicated as S in Fig. 3, maybe further reduced to produce the desired form of metal sheet or metal strip for use in making transformers. If it be desired to make a sheet from the slab S, the slab is cut into sections oi. the desired size, and the end portions are marked so that they may be identified as mentioned above, in order that the sections may be rolled longitudinally in the same sense as the original ingot was rolled, i. e., from A to B.

pass around the blooming mill, may be used to 50 The elongated metal M may be further passed between the rolls I and 2 a suitable number of times to produce the bloom P of Fig. 2, and the bloom may be reduced by further hot rolling betweenthe rolls I and 2' to the slab S of Fig. 3,- or to a bar of suitable. size, if desired, having end portions A and B which respectively correspond to the end portions A and B of the ingot.

It is to be noted that, in all passes through the rolling mills after the hot ingot has been initially introduced into the first hot roll mill, a reduction in thickness oi the metal is caused when the end portion A of the metal first enters the rolls While the sections from the slab or bar S may be cross rolled, according to the usual practice, to make silicon steel sheets, it is preferable to continue the rolling for forming sheets in the same sense.

The slab S is particularly adaptable for the rolling of long strips of metal which may be readily wound spirally to the desired shape to form transformer, cores. To accomplish this, the slab S, if large, may be divided into sections of theproper size or weight to give the desired length of a strip of given 'width and thickness.

In cutting the slab S into sections of the desired weight it is preferable to have the cut so made that the cut itself will designate the A and, B ends 01 the sections. This can be accomplished in various ways. a very convenient method of doing it being to use a wide angle V-shaped shear blade which will give the B end of the ,section the appearance of what is frequently termed a fish tail," and the end A is slightly pointed, so that any operator may readily see by inspection the pointed end of the section,

which is the one to be entered in the roll. Furthermore, as the rolling proceeds from this point on to the long strip, this marking by the shear is. not obliterated through any rolling process.

In Fig. 3a the bar Sis shown as having a section cut therefrom, the out s being in the form of -a wide angle V, the pointed end being designated A, andthe other end B.

The material from the rolls I and 2', which has been reduced to a suitable size and shape, is

then further reduced through rolling mills. For

Theslabor bar 8 is received from the slabbing mill at relatively high temperature, and subsequent heating is usually unnecessary before it is presented to the continuous hot rolls. As shown in Fig. 4, there are three pairs of reducing rolls. The rolls 3' and l are preferably spaced so as to produce a relatively high reduction in the thickf After suitable rolling in such a mill, the metal has a thickness, such as about .1". The relative speeds of the rolls 3 and 4, 5 and 6, and 1 and 8, are preferably adjusted to compensate for the elongation produced, and during the rolling procedure the material may be passed through suitable normalizing zones, pickling baths, etc., as is apparent to those skilled in the art.

The metal from the rolls 1 and 8 is ordinarily about .1" thick, and may be reeled or coiled as shown in Fig. 4, or, if desired, it may be continuously passed through annealing zones and further pairs of rolls, to produce amaterial of desired thickness. The material is coiled as shown in Fig. 4, and it should be unwound and recoiled, so that the end A of the coiled material, which corresponds to the end A of the slab S, is on the outside of the coil and may be entered first in subsequent rolling operations. To decrease the brittleness of the material, the coil R of Fig. 4 is heated to a suitable temperature, which may be accomplished by immersing it in boiling water while unwinding it and rewinding to form the coil T, shown in Fig. 6. During the recoiling process, or at any suitable time, the strip may be slit or cut to the width desired for subsequent rolling. It may then be reduced to the thickness desired by further rolling, preferably hot rolling.

Before further reducing the thickness of the strip material of coil T, the entire coil is preferably heated in a suitable furnace to a suitable annealing temperature, such as in the vicinity of 1600 to 1800" F., and it is then reduced in thickness in .a mill having three or more sets of rolls,

such as rolls 9 and I0, II and I2, and I3 and II, I

of Fig. 7. The rolls of the mill should be-adjusted so that the greatest reduction in the thickness of the material occurs between the rolls 9 and I0, and a successively smaller reduction occurs between rolls II and I2, and I3 and II, respectively.

It is contemplated that the metal be normalized or heat treated at suitable points intermediate the rolling operations to maintain .its temperature at the desired value. If the material from the continuous hot mill of Fig. 7 is of suitable thickness for use, it may be wound upon a form having the desired shape, such as that of coil N of Fig. 7.

For electrical purposes the steel processed in accordance with the above description should contain 3% or more of silicon. Improved electrical properties are obtained with increa'sed silicon content, but brittleness of the material likewise increases, so that the metal, when cold, becomes quite hard and brittle when 7% or 8% silicon is used. If the sheet steel as produced in the above process is to be flexed or bent cold, the silicon content should not exceed about 6%. If, however, the metal is hot rolled throughout and is hot coiled in the desired shape and size, a higher silicon content might be used.

The steel produced according to my invention in sheet-like form, i. e. in the form of sheets or strips, has increased magnetic permeability and decreased hysteresis loss over steels having equal silicon content formed "byprevious processes. These improved magnetic properties are obtained by the process disclosed herein, whereby proper directional crystal axis orientation has been controlled throughout the entire working of the sheet or strip.

Effects of unidirectional rolling, or-.rolling in one sense, and effects of back-and-forth rolling are diagrammatically illustrated in Figs. 8, 9 and 10 of the drawings. In Fig. 8 the unrolled ingot metal. I8, having vertical identifying lines I9 thereon, which are spaced uniformly so that flow of the metal may be indicated, is shown as the ingot is passed between reducing rolls I6 and I! in a direction from A to B to reduce its thickness. The straight identifying lines become curved, as shown at lBa. In Fig. 9 the metalwhich was reduced in Fig. 8 is shown when given a further reduction in the same sense. It may be seen that this further reduction causes the flow of the metal to continue in the, same relative direction as in Fig. 8, with the result that the flow lines l9a become more sharply curved, as shown at liib, and this becomes more pronounced on further reductions.

In Fig. 10 is illustrated metal from Fig. 8 which is reduced to the same extent as in Fig. 9, by rolling it in the opposite sense. The flow lines I 9a become distorted and reversed, as at l9c, showing a reversal of flow of the metal, which destroys proper crystal axis orientation, with resulting inferior magnetic properties.

Thus, Figs. 8 and 9 diagrammatically indicate the movement of metal when subjected to compression ,rolls in two rolling operations. From the rolling of the ingot to the finished strip, however, there are usually more than 20 or 30 such passes, and, as such passes are made while the metal is hot, the repeated elongations of the metal in the same sense tend to produce a moreuniform crystal axis orientation or grain arrangement. Such crystal axis orientation or grain arrangement seems to be characteristic of metal treated in this manner, and such metal possesses high magnetic properties.

Fig. 10 illustrates the detrimental effects of a single pass back and forth, which obviously tends to cause a non-uniform or heterogeneous structure, and such structure is emphasized when further back and forth passes are made, resulting in decreased magnetic properties.

The thickness of silicon steel for making of transformers or the like, whether the steel be in the form of sheets or strips, should preferably be about .0l4f. While the rolling of sheets by the pack rolling method enables one to obtain sheets of such a thickness, it has not been the practice to roll a strip by the hot rolling process to-such a gauge. Usually, hot rolling of strips has been carried to the point of about .03" in thickness in the regular practice. However, it is possible to roll hot strips to a thickness less than .02", such as the thick'.014", by passing the strip through a continuous heating zone in which temperatures are controlled and the distances from the rolls to the heating zones are regulated to preserve the heat of the. strip during its deformation and reduction. By passing'the'strip through a sufficient number of pairs of reducing rolls while it is still hot, and before it 'is allowed to cool below the proper rolling temperature, reduction to thickness of about .014. can be made. The number of beatings and the number of rolls used depend upon the character and silicon content of the steel and the amount of reduction desired.

As hereinbefore explained, finished sheets or strips of silicon steel having the'most improved magnetic properties are obtained when the metal is rolled in the same sense, i. e.,' from A'to' B, from the first rolling of the ingot to the last rolling of the finished sheet or strip. By this method the elongation of the metal being rolled or reduced always takes place in the same sense.

reverse pass on these mills is usually more deleterious to the magnetic properties, in that such reverse passes seem-to disturb the cry tal axis orientationof the resultant strip or eet to ,a greater degree than passes in which light reductions of the metal are made. It is therefore desirable that nearly all the passes in which substantial reductions are made be in the same sense as the first rolling of the ingot.

After the metal has been reduced to a slab or bar, of a suitable thickness for further processing into a sheet or strip, the reductions in thickness for a given rolling pass are, of course, considerably less in amount than those for forming the slab or bar. Even in the further processing, the metal should be rolled in a single sense to obtain the best properties, and particularly for the heavier reductions in thickness. If a slab or bar that has been produced by back-and-forth rolling is further reduced to a thin strip or sheet by rolling in a single sense, the magnetic properties are improved, but, as explained above, the best improvement appears to be accomplished when the rolling by which any substantial reduction in thickness is made is done in a single sense, i. e.,

from A to B.

'It is to be noted that in the trade the terms slab, billet and bar are frequently used to refer to steel sections of substantially the same thick-,

properties are attained by the characteristic crystal axis orientation or grain arrangement. produced by the rolling of the metal substantially in the same sense from the initial rolling of the ingot to the finished sheet or strip. Since all of the rolling may be accomplished while the metal is hot. the manufacture of such thin silicon steel sheet or strip is facilitated and the sheets or strips may be produced-at relatively lower cost.

The principles oi the present-invention may be utilized in various ways, numerous modifications and alterations being contemplated, substitution of parts and changes in construction being resorted to as desired, it being understood that the embodiments shown in the drawings, and described above, are given merely for purposes of explanation and illustration, without intending to limit the scope of the claims to the specific details disclosed.

What I claim is:

1. A process for producing relatively thin silicon steel having improved magnetic properties, I

. con steel having improved magnet c prope t able thickness, several laminae of the material may be superimposed and given the final reductions in the superimposed condition. Just be- ,'fore the final thickness of the material is obtained, the material is preferably heated to a bright orange heat and then given one or two light passes to reduce it to final thickness.

Because of the pressures necessary, it is usually considered impracticable to produce silicon sheet steel having more than about 3%% silicon present by cold rolling procedure. It may be seen, howev r, that, since theimproved magnetic properties f the invention areobtained'by hot rolling, a much larger silicon content may be present.

Steel rolled unidirectlonally, as disclosed herein, and having 3% or more silicon content. may be given a cold roll reduction to further improv its magnetic properties. When theste'el has a sufficiently low silicon content, if desired, it may be considerably reduced by cold rolling to the desired thickness, It will be seen that the silicon steel sheet or strip, produced according to the method disclosed herein, has improved magnetic properties and a relatively low watt loss, and it appears that these which comprises casting an ingot of steel with the desired silicon content, reducing the metal ner, whereby silicon steel in sheetlike form, having all effective elongation in a single sense, is produced.

3. A process for producing relatively thin sili' con steel having improved magnetic properties, which comprises casting an ingot of steel with the desired silicon content, reducing the metal of the ingot to slab thickness by rolling in a single longitudinal direction by always entering the metal elongated in a single longitudinal direction, and characterized by the elongated portions of i the grains continuously converging toward the" ends thereof, and the ends being sharply curved.

OTHO M. o'r'rE. 

